Self-Standing Container

ABSTRACT

A petaloid base for a self-standing container has an approximately hemispherical underlying base contour and a plurality of ovoid foot formations that interrupt and project from the underlying base contour to define a corresponding plurality of feet. Its shape resists stress cracking, maximises capacity relative to the height of the container and reduces the surface area of the base and hence material usage in comparison with equivalent known designs.

This invention relates to self-standing containers, more specifically to a petaloid base for such a container. Such containers may be blow-moulded of plastics material such as polyethylene terephthalate (PET).

As will be understood in the art, the generic term ‘PET’ includes compositions that predominantly contain polyethylene terephthalate—but may also including other materials. For example, a suitable composition may comprise approximately 95% polyethylene terephthalate and 5% nylon. As is known in the art, these materials may be mixed, or provided in different layers, for example via multilayer injection moulding and overmoulding.

Blow-moulded PET containers have long been used as bottles for beverages. More recently, they have been proposed for use as kegs for transporting, storing and dispensing beverages such as beer. An example of such a keg is disclosed in WO 2007/064277.

The example of WO 2007/064277 is given for background reference only: the broad concept of this invention is not limited to any particular use, material or method of manufacture of a container. However the invention has particular advantages in the context of thin-walled blow-moulded containers of the type apt to be manufactured from PET. It is in that context that the invention will be described in this specification.

Early PET containers had a plain hemispherical base and were rendered self-standing by the attachment of a separate base moulding to the base. Whilst a hemispherical base is simple, light and strong in isolation, the addition of a separate base moulding increases material and production costs and may hinder recycling.

To make a PET container self-standing without recourse to a separate base moulding, it is now well known to provide the container with an integrally-moulded petaloid base. The term ‘petaloid’ refers to a multi-footed base shape whose feet are disposed in an angularly-spaced arrangement around the base, the resulting shape resembling the petals of a flower when viewed from under the container in use. The container usually has a cylindrical side wall of circular horizontal cross-section, in which case the feet typically lie on a contact circle that is concentric with, and whose diameter is smaller than, the circular cross-section of the side wall. The feet act together to provide a stable multi-point support for the container.

There is continual pressure in the art of containers to reduce material and production costs and to ease recycling. Not only has this led to the adoption of one-piece containers with petaloid bases, but efforts continue to improve the petaloid base so that containers can be produced more economically while still performing reliably during storage, transportation and use. It is particularly desirable to reduce the amount of material necessary to give the container sufficient integrity and stability for commercial use. Even a small saving of material per container has a massive effect on the cost of production when reproduced across potentially tens to thousands of millions of containers per annum.

The correct trade off between the amount of material used and the integrity of the container is especially important when the container is to be used as a pressurised vessel. For example, the container may be used for storing, transporting and dispensing effervescent beverages such as beer. The beverage itself may be carbonated, or a propellant gas may be injected into the container at super-atmospheric pressure to force the beverage out of the container. Such a container needs to withstand these internal pressures under a range of environmental conditions. As well as withstanding internal pressures, the container needs to survive rough handling during transportation of the container.

It is against this background that the present invention has been devised. From one aspect, the invention resides in a petaloid base for a self-standing container, the base having a spheroidal underlying base contour and a plurality of spheroidal foot formations that interrupt and project from the underlying base contour to define a corresponding plurality of feet.

As the feet are spheroidal, it will be understood that their contact with a planar surface on which the base can rest is via a convex surface. Preferably therefore, contact between a given foot and that planar surface is via a point on the curved surface of that foot.

To maximise the capacity and strength of the container while minimising material usage, the underlying base contour is preferably substantially hemispherical. The contour may, for example, be that of an oblate spheroid whose polar axis coincides with a central axis of the base. For similar reasons, the foot formations are suitably elongate, such as partial ellipsoids or prolate spheroids. In preferred embodiments of the invention, the foot formations are ovoid (partially egg-shaped), in which case the contact points of the feet are most conveniently defined by the widest part of the cross-section of each foot formation being offset inwardly toward an inner end of the foot formation. In other words, the foot formations taper to a greater extent at their radially outer portions than their radially inner portions with respect to the central axis of the base.

Preferably, the base comprises formations, such as foot formations, whose shapes are substantially rotationally symmetrical about an axis. For example, shapes such as spheroids, ellipsoids and ovoids that define the foot formations are preferably substantially rotationally symmetrical about an axis. Advantageously, if these shapes that form the base are rotationally symmetrical, the material used to form these structures can be minimised. At the same time the internal capacity of the base, as well as its strength can be maximised.

To define feet with minimal usage of material, the elongate foot formations preferably have respective longitudinal axes, which axes lie in planes extending radially from a central axis of the base. Those axes of the foot formations suitably extend outwardly and upwardly in conical relation from the central axis of the base.

Each foot formation may have an elliptical, preferably ovate intersection with the underlying base contour. To reduce stress concentration, the intersection is preferably of concave cross section.

To strengthen the base, the foot formations preferably radiate from a central protrusion. That protrusion may be approximately polygonal, with a number of sides corresponding to the number of foot formations.

The foot formations are suitably separated by valleys, that may for example radiate from apices of the polygonal protrusion. To minimise material usage, the valleys preferably widen moving outwardly across the base. Each valley may, for example, have an inner and an outer section and the walls of the valley may diverge more sharply in the outer section than in the inner section. However, the walls of the valley may diverge in both the inner and the outer sections of the valley.

In plan view, each foot formation may have an enlarged central region from which the foot formation tapers inwardly across an inner portion to an inner end. In that case, the inner portions of the foot formations suitably lie in segmented relation around the base. To minimise material usage, it is preferred that in plan view, each foot formation tapers from the enlarged central region outwardly across an outer portion to an outer end of the foot formation.

The inventive concept extends to a container such as a keg or a bottle having the base of the invention. Preferably, the container is constructed by blow-moulding a preform, ideally made of PET.

Preferably, where the material used is PET, the container has an average pressure resistance to material usage ratio of greater than 3 MPa/kg. More preferably, the average pressure resistance to material usage ratio is greater than 3.75 MPa/kg. Also, preferably, the container has a capacity to material usage ratio of over 40 litres/kg. More preferably, the container has a capacity to material usage ratio of over 80 litres/kg.

In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings in which:

FIG. 1 is a plan view from underneath a container having a petaloid base in accordance with the invention;

FIG. 2 is a side view of the petaloid base of the container shown in FIG. 1;

FIG. 3 is a sectional side view through the petaloid base of the container shown in FIG. 1;

FIGS. 4( a), 4(b) and 4(c) are, respectively, an underneath plan view, a side view and a perspective view of a container having a base as shown in FIGS. 1 to 3, embodied in this example as a bottle of 0.33 litre capacity;

FIGS. 5( a), 5(b) and 5(c) are, respectively, an underneath plan view, a side view and a perspective view of another container having a base as shown in FIGS. 1 to 3, embodied in this example as a keg of 20 litres capacity;

FIGS. 6( a), 6(b) and 6(c) are, respectively, an underneath plan view, a side view and a perspective view of another container having a base in accordance with the invention, embodied in this example as a bottle of 1.5 litres capacity, the base of this example being a variant having seven feet;

FIG. 7 is the underneath plan view of the container as shown in FIG. 1 marked in this instance with section lines referred to in FIGS. 8 and 9;

FIG. 8 is an enlarged partial sectional side view through the petaloid base of the container of FIG. 7, taken along section line VIII-VIII;

FIG. 9 is an enlarged partial sectional side view through the petaloid base of the container of FIG. 7, taken along section line IX-IX;

FIG. 10 is a side view of a container having a five-footed petaloid base as shown in FIGS. 1 to 3, embodied in this example as a keg having a non-cylindrical side wall, and of 18-litre capacity;

FIG. 11 is a side view of a plastics preform for blow moulding into the 18-litre capacity keg as shown in FIG. 10; and

FIG. 12 is an enlarged sectional side view of the container base as shown in FIG. 3, together with a beverage dispensing tube within the container.

Referring firstly to FIGS. 1 and 2 of the drawings, a container 10 in this example of the invention comprises a hollow body of blow-moulded PET. The body of the container 10 is of circular horizontal section, the radius of that circle extending orthogonally from a central longitudinal axis 12 that extends centrally through the closed base 14 of the container 10. Above the base 14, but not shown in FIGS. 1 and 2, is a substantially cylindrical side wall surmounted by a neck portion. The side wall is integral with and terminates at its lower end in the base 14; in turn, the side wall is integral with and terminates at its upper end in the neck portion at the top of the container 10.

The fundamental or underlying shape of the base 14 is a slightly flattened hemisphere, that hemisphere being rotationally symmetrical about the central longitudinal axis 12 of the container 10. More generally, the underlying shape of the base 14 is an oblate spheroid, being a rotationally symmetric ellipsoid having a diameter on its polar axis (coinciding with the central longitudinal axis 12) that is shorter than the diameter of the equatorial circle whose plane bisects it. This approximately hemispherical shape maximises resistance to internal pressure, reduces stress concentrations to resist cracking, and also maximises internal volume while minimising material usage.

In accordance with the invention, the base 14 further includes integrally-moulded blister-like feet disposed in a petaloid arrangement around the base, the feet being defined in this example by five hollow ovoid foot formations 16 that radiate equiangularly from a relatively shallow generally pentagonal convex protrusion 18 on the central longitudinal axis 12. More generally, the foot formations 16 are elongate ellipsoids in the form of prolate spheroids, a prolate spheroid being a spheroid whose diameter along its polar axis is greater than its equatorial diameter.

The polar axes 20 of the spheroidal foot formations 16 extend outwardly and upwardly in equi-angularly spaced radially-disposed planes from the central longitudinal axis 12 of the container 10. Thus, the polar axes 20 of the foot formations 16 (see FIG. 2) lie on a virtual frusto-conical surface surrounding the central longitudinal axis 12.

Circumferentially adjacent pairs of foot formations 16 are separated by valleys 22 that radiate equi-angularly from the apices 24 of the pentagonal central protrusion 18. The valley floors follow the spheroidal shape of the base 14 and open at their outer ends to an outer portion of the base 14 that lies radially outwardly beyond the foot formations 16. Furthermore, each foot formation 16 and the central protrusion 18 are joined via a transition portion that curves smoothly without distinct transitions or discontinuities. Thus, as shown in FIG. 3, a foot formation 16, the smoothly curving transition portion and the central protrusion 18 together define a sinuous cross section.

Also as shown in FIG. 3, the convex central protrusion 18 has a radius of curvature r that is smaller than the general radius of curvature R of the spheroidal base 14: thus R>r. Moreover, the convex central protrusion 18 extends to a level beyond—and thus, in use, below—the lowermost apex of the underlying base contour. Also, the convex central protrusion 18 extends to a level within—and thus, in use, above—the extent of the foot formations 16.

The foot formations 16 bulge outwardly from the underlying spheroidal contour of the base 14 by virtue of an ovoid convex wall. The convex wall of each foot formation 16 is surrounded by a concave transition zone 26 in the shape of an ovate ring. The transition zone 26 extends smoothly into the spheroidal wall of the base with a large radius of curvature to reduce stress concentration and hence to minimise stress cracking. The transition zones 26 of circumferentially adjacent foot formations 16 partially define the valley 22 between those foot formations 16.

Each foot formation 16 is generally elliptical (in this example, ovate) in underneath plan view, reaching a maximum width in an enlarged central region 28 between its inner end 30 and its outer end 32. Thus, each foot formation 16 tapers in opposite directions from the widest part of the central region 28: along an inner portion 34 moving inwardly toward the central longitudinal axis 12 to the inner end 30; and along an outer portion 36 moving outwardly away from the central longitudinal axis 12 to the outer end 32.

In underneath plan view, the inwardly-tapering inner portions 34 of the foot formations 16 fit closely between their neighbours around the circular base 14 like segments of an orange. These inner portions 34 of the foot formations 16 alternate with, and are separated by, narrow inner sections 38 of the valleys 22, which may be approximately parallel but, in this example, widen slightly as they extend outwardly from the pentagonal central protrusion 18. However where they extend outwardly into their outer sections 40 beyond the widest part of the foot formations 16, the valleys 22 widen near-exponentially between the tapering outer portions 36 of the foot formations 16 until they reach a maximum width between the outer ends 32 of adjacent foot formations 16.

Thus, moving along the valleys 22 from the central longitudinal axis 12 toward the outer diameter of the base 14, the gap between the foot formations 16 increases. In contrast, in a previously-known petaloid base such as that disclosed in EP 0671331, this gap decreases.

Viewed now from the side, the foot formations 16 extend to a level beyond—and thus, in use, below—the lowermost apex of the base 14 defined by the central pentagonal protrusion 18. The foot formations 16 all extend to the same level. Thus, at that level, each foot formation 16 defines a contact point 42 that will lie stably upon a flat support surface (not shown) orthogonal to the central longitudinal axis 12 of the container 10.

FIG. 3 shows that the foot formations are somewhat egg-shaped with the widest part of their cross-sections offset slightly inwardly and downwardly toward their inner ends 30.

The contact points 42 of the foot formations 16 are equi-spaced on and around a contact circle centred on the central longitudinal axis 12 of the container 10. The diameter (x) of the contact circle relates to the side wall diameter (Dy) of the container 10 in a ratio as follows:

$\frac{Dy}{0.5x} = k$

In accordance with the invention, k is preferably between 3.6 and 5.5, more preferably between 4.0 and 5.3, still more preferably between 4.2 and 5.0 and typically 4.7. This may be contrasted with typical PET bottles on the market whose corresponding ratio k is typically 2.5 to 3.5. The relatively large value for k in the invention stems from a relatively small value for x. This is advantageous because a small contact circle creates a small—and hence inherently stiff—diaphragm between the contact points 42.

The result is a central area within the contact circle between the contact points 42 of the foot formations 16 that is quite rigid and hence resistant to movement during internal pressure, up to burst pressure. The rigidity of the area within the contact circle is enhanced by the undulating wall section defined by the inner portions 34 of the foot formations 16, the valleys 22 between them, and the central protrusion 18.

Stiffness within the contact circle is important not just for a high burst pressure but also for stability. This is because the lowest point on the central longitudinal axis (the lowermost apex of the base 14 defined by the central pentagonal protrusion 18) will tend to be pushed down under internal pressure. If that lowest point moves so far as to contact a supporting surface in use, the container cannot rest stably on the contact points 42 of the foot formations 16. The stiffness of the base shape of the invention means that compared to previously known designs, the distance from the central apex of the base to a supporting surface is relatively small, to the benefit of stability and capacity relative to the height of the container.

Viewing any one foot formation 16 end-on (i.e. from the side of the container 10 looking inwardly towards the central longitudinal axis 12), the contour of that foot formation 16 describes a substantially constant convex radius between the concave radii of the transition zones 26 to each side. A conventional petaloid base typically has flatter surfaces defining a V-shaped valley between the feet, to the detriment of material usage and stress concentration. Stress concentrations create areas of a container that are particularly vulnerable to rupture under high internal pressure.

The arrangement of the base 14 of the present invention is particularly suited to containers for dispensing liquids under pressure. In particular, the increased value for k makes the base stiffer and hence better suited for retaining stability whilst the container is subject to high internal pressure. Furthermore, by increasing the value of k, it is possible to have the convex central protrusion 18 positioned axially lower than would otherwise be possible for a container that is subject to high internal pressure. This can maximise the quantity of beverage that can be practically dispensed from the container 10. This advantage is discussed with reference to FIG. 12 in which is shown the same sectional side view of the container base 14 of FIG. 3, together with a beverage dispensing tube 120.

In this context, the container is used as a beer keg 10 that is provided with a closure assembly that is sealed on to the tubular neck of the keg 10 in a push-fit arrangement. The tube 120 is coupled to the closure assembly (not shown) and extends from it along the central longitudinal axis 12 into the base of the keg 10. The axially lower end of the tube 120 extends into the central protrusion 18. The end of the tube 120 sits within the central protrusion 18 and hangs just inside the apex of the central protrusion 18, thereby providing an annular gap through which a beverage can pass from the keg 10 into the tube 120 or visa-versa. The shape of the central protrusion 18 also enables the axially lower end of the tube 120 to be correctly located and retained within the central protrusion during fitting and use.

In use, when dispensing a beverage, the keg 10 is maintained in an upright position. The closure assembly allows a pressurised gas to be introduced into the headspace of the keg 10 to force the beverage out through the tube 120. As the axially lowermost end of the tube 120 is located within the central protrusion 18, and the central protrusion 18 is disposed at a relatively low axial position within the keg 10, this ensures that almost all of the beverage within the keg 10 can be extracted from it.

It may be possible to further increase the amount of beverage that can be practically extracted from the keg 10 by extending the tube 120 into one of the foot formations 16. In such an arrangement, the tube 120 would need to bend away from the central longitudinal axis 12 at its lower end. Although this may marginally increase the amount of beverage that can be dispensed from the keg 10, this can complicate process of fitting the closure assembly and tube 120 to the keg 10. In particular, inserting a bent tube 120 into the keg 10 can require a complicated automated fitting process. Furthermore, the bending of the tube 120 away from the central longitudinal axis 12 can subject the closure assembly to which the tube 120 is attached at its axially upper end to uneven forces. This can reduce the reliability of the closure assembly, which is of particular concern when the keg 10 is subject to high internal pressure.

The petaloid base of the invention may be applied to a wide range of containers such as bottles and kegs. FIGS. 4( a), 4(b) and 4(c) and FIGS. 5( a), 5(b) and 5(c) show a five-footed base of the invention applied, respectively, to a bottle 44 of 0.33 litre capacity, which may typically be used for carbonated soft drinks, and a keg 46 of 20 litres capacity, which may typically be used for beer. These drawings show features omitted from FIGS. 1 and 2, namely a substantially cylindrical side wall 48 surmounted by a neck portion 50. The side wall 48 is integral with and terminates at its lower end in the base 14; in turn, the side wall 48 is integral with and terminates at its upper end in the neck portion 50 at the top of the container.

FIG. 10 shows a further five-footed base of the invention applied to a keg 104 of 18-litre capacity with a non-cylindrical side wall 108. In this example, the side wall 108 is convex, rotationally symmetrical about the central longitudinal axis of the keg 104 and so generally follows the shape of an ovoid. At its axially lower end portion, the side wall curves smoothly into the spheroidal underlying contour of the base of the present invention. At its axially upper end portion, which tapers to a greater extent than the axially lower end portion, the side wall curves smoothly into the concave neck of the keg 104. The convex side wall 108 is shaped in this way to maximise internal pressure resistance, maximise the internal capacity of the keg 104 and minimise material usage. FIG. 11 is an enlarged side view of a plastics preform for blow moulding into the container as shown in FIG. 10.

Other variations of the invention are possible without departing from the inventive concept. For example, a variant of the base of the invention shown in FIGS. 6( a), 6(b) and 6(c) is applied to a bottle 52 of 1.5 litres capacity. This variant has seven foot formations 54 instead of five, with a generally heptagonal central protrusion 56 between them. Like the five-footed base variant, seven-footed base variants can be applied to any size of container, such as bottles of 0.33 litres, 0.5 litres, 1 litre, 1.5 litres or larger, and kegs of 20 litres or other capacities.

An odd number of feet is preferred for optimum stability, there being at least three feet (in which case the central protrusion is generally triangular) but preferably not more than seven feet; five or seven feet are considered optimal.

To put the invention into context but without limiting its broadest scope as defined in the claims, various dimensional characteristics will now be given by way of example.

Firstly, the table below sets out a volume comparison between a conventional base and a base in accordance with the invention, assuming in this instance that the base defines five feet. Volumes in the table are expressed in millilitres (ml). The volume refers to the internal volume of the base, defined as the portion of the container below the cylindrical side wall of the container. It will be noted that the base of the invention has a volume approximately five times greater than the volume of a conventional petaloid container base, to the benefit of compactness and material usage for a given container capacity.

Container with five feet Conventional base Base of the invention   20 litre keg, dia 235 mm 128 (20%)  634 0.33 litre bottle, dia 60 mm 2.7 (18%) 15  0.5 litre bottle, dia 65 mm 3.5 (18%) 19  1.0 litre bottle, dia 80 mm 6.5 (18%) 36  1.5 litre bottle, dia 95 mm  11 (20%) 55

Secondly, the following dimensions help to define the base shape for each of the above capacities of container:

Radius Radius of transition from of underlying underlying base contour Container with five feet base contour to side wall   20 litre keg, dia 235 mm 135.0 mm  49.6 mm 0.33 litre bottle, dia 60 mm 34.5 mm 19.1 mm 0.5 litre bottle, dia 65 mm 37.4 mm 20.7 mm  1.0 litre bottle, dia 80 mm 46.0 mm 25.4 mm  1.5 litre bottle, dia 95 mm 54.6 mm 30.2 mm

Radial projection of foot Diameter formations beyond radius of of contact Container with five feet underlying base contour circle   20 litre keg, dia 235 mm 18.1 mm  99.9 mm 0.33 litre bottle, dia 60 mm 5.3 mm 28.6 mm  0.5 litre bottle, dia 65 mm 5.5 mm 31.0 mm  1.0 litre bottle, dia 80 mm 7.1 mm 38.1 mm  1.5 litre bottle, dia 95 mm 8.4 mm 45.3 mm

Width of foot formations Length of foot formations across Container with five feet along polar axis* polar axis*   20 litre keg, dia 235 mm 80.2 mm 59.5 mm 0.33 litre bottle, dia 60 mm 22.9 mm 15.6 mm  0.5 litre bottle, dia 65 mm 24.8 mm 16.9 mm  1.0 litre bottle, dia 80 mm 30.6 mm 20.8 mm  1.5 litre bottle, dia 95 mm 36.3 mm 24.7 mm *Including transition zone

Radius Radius of transition from of underlying underlying base contour Container with seven feet base contour to side wall   20 litre keg, dia 235 mm 135.0 mm  49.6 mm 0.33 litre bottle, dia 60 mm 34.2 mm 18.9 mm  0.5 litre bottle, dia 65 mm 37.3 mm 20.7 mm  1.0 litre bottle, dia 80 mm 46.2 mm 25.6 mm  1.5 litre bottle, dia 95 mm 54.6 mm 30.2 mm

Radial projection of foot Diameter formations beyond radius of of contact Container with seven feet underlying base contour circle   20 litre keg, dia 235 mm 18.1 mm  99.9 mm 0.33 litre bottle, dia 60 mm 5.3 mm 28.5 mm  0.5 litre bottle, dia 65 mm 5.8 mm 31.0 mm  1.0 litre bottle, dia 80 mm 7.2 mm 38.5 mm  1.5 litre bottle, dia 95 mm 8.4 mm 45.4 mm

Width of foot formations Length of foot formations across Container with seven feet along polar axis* polar axis*   20 litre keg, dia 235 mm 78.9 mm 54.8 mm 0.33 litre bottle, dia 60 mm 22.4 mm 14.0 mm  0.5 litre bottle, dia 65 mm 24.4 mm 15.3 mm  1.0 litre bottle, dia 80 mm 30.3 mm 19.0 mm  1.5 litre bottle, dia 95 mm 35.7 mm 22.4 mm *Including transition zone

Radius of transition zone Radius of transition zone (five feet) (seven feet)   20 litre keg, dia 235 mm 12.0 mm  8.0 mm 0.33 litre bottle, dia 60 mm 3.15 mm 1.88 mm  0.5 litre bottle, dia 65 mm 3.44 mm 2.05 mm  1.0 litre bottle, dia 80 mm 4.26 mm 2.54 mm  1.5 litre bottle, dia 95 mm  5.0 mm  3.0 mm

FIGS. 7 to 9 provide additional dimensional information relating to a 20-litre keg having a five-footed base 14. FIGS. 10 and 11 respectively show dimensional information relating to an 18-litre keg 104 having a five-footed base and its preform 106.

FIG. 8 shows a partial sectional side view through the petaloid base of the 20-litre keg of FIG. 7, taken along section line VIII-VIII. The resulting section plane intersects a foot formation 16 at its contact point 42, and is parallel to and is radially-spaced at a distance of 50 mm from the central longitudinal axis 12 of the keg 10. At this section of the foot formation 16, its contour is a substantially constant convex radius of 23.0 mm between the concave radii of 12.0 mm of the transition zones 26 to each side.

FIG. 9 is a partial sectional side view through the petaloid base of the 20-litre keg of FIG. 7, taken along section line IX-IX. The resulting section plane is aligned with the central longitudinal axis 12 of the keg 10, and intersects the same foot formation 16 as shown in FIG. 8 at its contact point 42. The view shown in FIG. 9 corresponds to the view shown in FIG. 3, but provides the following additional dimensional information relating to the 20-litre keg:

RADIUS DATA Radius of underlying base contour 135.0 mm  Radius of convex central protrusion 35.0 mm Radius of concave transition zone between the convex 12.0 mm central protrusion and the radially inner end of a foot formation Radius of a foot formation at a position on the inner portion 35.0 mm adjacent the radially inner end Radius of a foot formation at a position on the inner portion 43.0 mm between the radially inner end and the central region of the foot formation Radius of a foot formation at a position on the central 50.0 mm region between the contact circle and the inner portion Radius of a foot formation at a position on the central 20.5 mm region that is radially inner of and adjacent to the contact circle Radius of a foot formation at a position on the central 24.0 mm region that is radially outer of and adjacent to the contact circle Radius of a foot formation at a position on the central 32.0 mm region between the contact circle and the outer portion Radius of a foot formation at a position on the outer portion 27.75 mm  between the radially outer end and the central region of the foot formation Radius of a foot formation at a position on the outer portion 120.0 mm  adjacent the radially outer end of the foot formation Radius of concave transition zone between underlying base 12.0 mm contour and radially outer end of a foot formation Radius of transition from underlying base contour to side 49.6 mm wall

These radius measurements are also applicable to points on other foot formations 16 of the container 10. These points typically lie within any one of the planes aligned with both the central longitudinal axis 12 of the container and a polar axis of a given foot formation 16.

DISTANCE DATA Distance along central longitudal axis between convex 3.0 mm central protrusion and plane containing the contact circle Axial depth of convex central protrusion along central 4.5 mm longitudinal axis Distance along central longitudinal axis from underlying 8.0 mm base contour to plane containing the contact circle Distance along axis aligned with central longitudinal axis 7.5 mm from transition zone (between central protrusion and a foot formation) to plane containing the contact circle Axial depth of the base portion (i.e. axial distance from 91.2 mm  plane containing the contact circle to axially lower end of cylindrical side wall) Radial length from central longitudinal axis to transition 84.66 mm  between base contour and foot formation

In addition to dimensional data, the following data derives from pressure tests indicating the typical burst pressure of the 20-litre keg 10 having a five footed petaloid base 14 according to the present invention. By way of comparison, pressure tests were also carried out on a conventional petaloid base under similar conditions. The values represent the burst pressure in bar.

Conventional Base burst pressure Base of the invention burst Test (bar) pressure (bar) 1 9.29 9.55 2 7.68 9.04 3 9.09 8.59 4 8.92 9.57 5 8.8 9.29 6 5.99 7.78 7 5.96 8.69 8 6.25 8.08 9 9.14 9.31 10  8.82 8.33 AVG 7.99 8.82 MAX 9.29 9.57 MIN 5.96 7.78 DIFF 3.33 1.79

Thus, it can be seen that the average burst pressure of the 20-litre keg having a five-footed base is approximately 8.8 bar=880 kPa. Furthermore, the material usage of the litre keg corresponds to 0.234 kg of PET. Accordingly, ratios directed to the pressure resistance, capacity and material usage can be derived for this 20-litre keg:

-   -   Average pressure resistance to material usage ratio=3.76 MPa/kg     -   Capacity to material usage ratio=85 litres/kg

It will be understood that similar ratios can be extrapolated for containers of different shapes and sizes, but also incorporating the base 14 according to the present invention.

FIG. 10 provides additional dimensional data corresponding to the 18 litre keg 104:

Convex radius of underlying base contour 135.0 mm Diameter of body at widest point 287.0 mm Convex radius of body contour 352.0 mm Convex radius of contour between body and neck 185.0 mm Concave radius of neck contour  65.0 mm Diameter of neck  65.0 mm Total axial length 490.0 mm Axial length from base to neck collar 472.0 mm Axial length from keg opening, to beverage fill point (FP) 112.5 mm mark - denoting an 18 litre fill from a level base

FIG. 11 provides additional dimension data corresponding to the preform 106 of the 18 litre keg 104 of FIG. 10:

Total axial length 195.0 mm  Axial length from base to neck collar 177.0 mm  Axial thickness of base  6.0 mm Thickness of each cylindrical side wall 11.0 mm Axial length of cylindrical neck portion below neck collar 15.0 mm Axial length of neck portion from below neck collar to 57.3 mm cylindrical side wall (including cylindrical neck portion and frustoconical neck portion) Diameter of cylindrical neck portion 64.2 mm Diameter of cylindrical side wall 77.0 mm Internal bore diameter of the preform 55.0 mm Diameter of the neck collar 81.0 mm

The approximate burst pressure of this 18-litre keg having a five-footed base is approximately 14 bar=1400 kPa. The material usage of the 18-litre keg corresponds to 0.468 kg of PET. Accordingly, ratios directed to the pressure resistance, capacity and material usage can be derived for this 18-litre keg:

-   -   Average pressure resistance to material usage ratio=˜3 MPa/kg.     -   Capacity to material usage ratio=41 litres/kg.

For a base with five feet, the following ratios apply in these examples:

-   -   For 20-litre keg:         -   Length of foot formations along polar axis/width of foot             formations across polar axis=1.35         -   Diameter of contact circle/width of foot formations across             polar axis=1.68         -   Radius of underlying base contour/diameter of side wall=0.57         -   Radius of underlying base contour/radius of transition from             underlying base contour to side wall=2.72         -   Radial projection of foot formations beyond radius of             underlying base contour/radius of underlying base             contour=1.13     -   For bottles of various capacities:         -   Length of foot formations along polar axis/width of foot             formations across polar axis=1.47         -   Diameter of contact circle/width of foot formations across             polar axis=1.83         -   Radius of underlying base contour/diameter of side wall=0.58         -   Radius of underlying base contour/radius of transition from             underlying base contour to side wall=1.81         -   Radial projection of foot formations beyond radius of             underlying base contour/radius of underlying base             contour=1.15

Similarly, for a base with seven feet, the following ratios apply in these examples:

-   -   For 20-litre keg:         -   Length of foot formations along polar axis/width of foot             formations across polar axis=1.44         -   Diameter of contact circle/width of foot formations across             polar axis=1.82         -   Radius of underlying base contour/diameter of side wall=0.57         -   Radius of underlying base contour/radius of transition from             underlying base contour to side wall=2.72         -   Radial projection of foot formations beyond radius of             underlying base contour/radius of underlying base             contour=1.13     -   For bottles of various capacities:         -   Length of foot formations along polar axis/width of foot             formations across polar axis=1.59         -   Diameter of contact circle/width of foot formations across             polar axis=2.03         -   Radius of underlying base contour/diameter of side wall=0.57         -   Radius of underlying base contour/radius of transition from             underlying base contour to side wall=1.8         -   Radial projection of foot formations beyond radius of             underlying base contour/radius of underlying base             contour=1.15

It will be apparent from the foregoing description that the improved petaloid base shape of the invention has various additional advantages. Its softly-curving shape with an absence of sharp radii is beneficial to resist stress cracking. Also, importantly, its surface area is less than equivalent known designs. Thus, for a given amount of resin, the invention allows a thicker wall and hence a stronger base. Alternatively it is possible to reduce weight and material usage while maintaining the strength of the base. A strong base is particularly important in applications where the containers are subjected to elevated internal pressure and/or elevated temperature, such as carbonated soft drinks, beer and hot-fill or pasteurised liquids. 

1. A petaloid base for a self-standing container, the base having a spheroidal underlying base contour and a plurality of spheroidal foot formations that interrupt and project from the underlying base contour to define a corresponding plurality of feet.
 2. The base of claim 1, wherein the underlying base contour is an oblate spheroid whose polar axis coincides with a central axis of the base.
 3. The base of claim 1, wherein the underlying base contour is substantially hemispherical.
 4. The base of claim 1, wherein the foot formations are elongate ellipsoids.
 5. The base of claim 4, wherein the foot formations are prolate spheroids.
 6. The base of claim 4, wherein the foot formations are ovoid, and wherein the widest part of the cross-section of each foot formation is offset inwardly toward an inner end of the foot formation.
 7. (canceled)
 8. The base of claim 4, wherein the foot formations have respective longitudinal axes, which axes lie in planes extending radially from a central axis of the base.
 9. The base of claim 8, wherein the axes of the foot formations extend outwardly in conical relation from the central axis of the base.
 10. The base of claim 9, wherein the axes of the foot formations extend outwardly and upwardly from the central axis of the base, and wherein the axes of the foot formations meet at the central axis of the base at a position axially below the base.
 11. (canceled)
 12. The base of claim 1, wherein each foot formation has an elliptical intersection with the underlying base contour, the intersection is ovate and of concave cross section. 13-14. (canceled)
 15. The base of claim 1, wherein the foot formations radiate from a central protrusion.
 16. The base of claim 15, wherein the central protrusion has a radius of curvature that is smaller than the radius of curvature of the underlying base curve, and wherein the central protrusion extends to a level beyond the lowermost apex of the underlying base contour.
 17. (canceled)
 18. The base of claim 15, wherein a foot formation and the central protrusion are joined via a smoothly curving transition portion, wherein the foot formation, the smoothly curving transition portion and the central protrusion together define a sinuous cross section, and wherein the transition portion defines a curve whose curvature is converse to the curvature of at least one of the foot formations and central protrusion. 19-20. (canceled)
 21. The base of claim 15, wherein the central protrusion is substantially convex with respect to the exterior of the container.
 22. The base of claim 15, wherein the central protrusion defines a recess with respect to the interior of the container, the recess being arranged to locate and retain a free end of a fluid delivery tube within the container.
 23. The base of claim 15, wherein the central protrusion is generally polygonal, with a number of sides corresponding to the number of foot formations, wherein the foot formations are separated by valleys, and the valleys radiate from apices of the polygonal protrusion.
 24. The base of claim
 1. 25. The base of claim
 15. 26. The base of claim 1, wherein the foot formations are separated by valleys, the valleys widen moving outwardly across the base, each valley has an inner and an outer section and the walls of the valley diverge more sharply in the outer section than in the inner section, and the walls of the valley diverge in both the inner and the outer sections of the valley. 27-28. (canceled)
 29. The base of claim 1, wherein in plan view, each foot formation has an enlarged central region that tapers inwardly across an inner portion to an inner end of the foot formation, the inner portions of the foot formations lie in segmented relation around the base, and each foot formation tapers from the enlarged central region outwardly across an outer portion to an outer end of the foot formation. 30-31. (canceled)
 32. A self-standing container having a base as defined in claim
 1. 33. The container of claim 32, wherein the foot formations of the base define respective contact points that together are spaced around a contact circle whose diameter (x) relates to a side wall diameter (Dy) of the container as: $\frac{Dy}{0.5x} = k$ where k is between 3.6 and 5.5.
 34. The container of claim 33, wherein k is between 4.0 and 5.3.
 35. The container of claim 34, wherein k is between 4.2 and 5.0.
 36. The container of claim 32, having an average burst pressure resistance to material usage ratio of greater than 3 MPa/kg.
 37. The container of claim 32, having a capacity to material usage ratio of greater than 40 litres/kg.
 38. The container of claim 32, comprising a fluid delivery tube aligned with a central longitudinal axis of the container, the tube extending between the base of the container and an opening of the container. 